Precision casting process

Abstract

A mold assembly for sand casting is disclosed. The mold assembly includes a drag having a first vertical axis and a first surface. The first surface extends generally perpendicular to the first vertical axis. The mold assembly also includes a cope having a second vertical axis positioned on the first surface such that the first vertical axis and the second vertical axis coincide to form a central vertical axis. The cope includes a second surface and a third surface both extending generally perpendicular to the second vertical axis. The mold assembly also includes a casting cavity disposed about the central vertical axis and located between the first surface and the second surface, and a core disposed about the central vertical axis and positioned in the casting cavity. The mold cavity further includes a pouring cup disposed about the second vertical axis and extending downward from the third surface to the casting cavity. The pouring cup is configured to deliver a substantial portion of liquid material at a time directly into the casting cavity without directing the liquid material through a choke point.

1 . A mold assembly for sand casting, comprising:
 a drag having a first vertical axis and a first surface, the first surface extending generally perpendicular to the first vertical axis;   a cope having a second vertical axis positioned on the first surface such that the first vertical axis and the second vertical axis coincide to form a central vertical axis, the cope including a second surface and a third surface both extending generally perpendicular to the second vertical axis;   a casting cavity disposed about the central vertical axis and located between the first surface and the second surface;   a core disposed about the central vertical axis and positioned in the casting cavity; and   a pouring cup disposed about the second vertical axis and extending downward from the third surface to the casting cavity, the pouring cup being configured to deliver a substantial portion of liquid material at a time directly into the casting cavity without directing the liquid material through a choke point.   
   
   
       2 . The mold assembly of  claim 1 , wherein the core is made of a ceramic material. 
   
   
       3 . The mold assembly of  claim 2 , wherein the core has a smooth surface finish. 
   
   
       4 . The mold assembly of  claim 1 , wherein a free space in the casting cavity not occupied by the core is substantially shaped like an impeller. 
   
   
       5 . The mold assembly of  claim 4 , wherein the core includes passageways substantially shaped like blades of the impeller. 
   
   
       6 . The mold assembly of  claim 1 , wherein the pouring cup has a shape substantially resembling a frustum of a cone. 
   
   
       7 . The mold assembly of  claim 6 , wherein a first end of the pouring cup forms an opening on the third surface and a second end of the pouring cup forms an opening on the second surface. 
   
   
       8 . The mold assembly of  claim 1 , wherein the pouring cup includes a shell defining a flow path into the casting cavity. 
   
   
       9 . The mold assembly of  claim 1 , wherein the casting cavity and the pouring cup are surrounded by packed sand. 
   
   
       10 . The mold assembly of  claim 1 , wherein the casting cavity includes a first cavity disposed on the drag and a second cavity disposed on the cope and the core is positioned on the first cavity. 
   
   
       11 . A method of sand casting a part, comprising:
 forming a casting cavity between a cope and a drag of a molding assembly, the casting cavity being located about a vertical axis of the molding assembly;   directing a substantial portion of liquid material at a time directly into casting cavity without directing the liquid material through a choke point;   shaping the liquid material in the casting cavity using a ceramic core; and   solidifying the liquid material in the casting cavity to form a casting having a shape substantially resembling the part.   
   
   
       12 . The method of  claim 11 , wherein the liquid material includes a molten liquid metal. 
   
   
       13 . The method of  claim 11 , wherein directing liquid material into the casting cavity along the flow path includes directing liquid material from a pouring cup coupled to the cope directly into the casting cavity. 
   
   
       14 . The method of  claim 13 , wherein directing liquid material into the casting cavity includes filling free space in the casting cavity with the liquid material, and holding a reserve of the liquid material in the pouring cup after the filling of the free space. 
   
   
       15 . The method of  claim 11 , wherein the part is an impeller and shaping the liquid material includes shaping the liquid material to form blades of the impeller having a smooth surface finish. 
   
   
       16 . The method of  claim 11  further including, removing the cast part from the molding assembly. 
   
   
       17 . The method of  claim 16 , wherein removing the cast part includes breaking the core to separate the cast part from the core. 
   
   
       18 . A method of creating a mold for sand casting a part, comprising:
 forming a casting cavity between packed aggregate material of a cope and packed aggregate material of a drag, the cope and the drag being parts of a molding assembly having a central vertical axis, and the casting cavity being disposed about the central vertical axis;   locating a pouring cup on the cope, the pouring cup being shaped substantially like a frustum of a cone and being configured to deliver a substantial portion of a molten liquid at a time to the casting cavity without directing the molten liquid through a choke point; and   positioning a ceramic core in the casting cavity such that the core is circumferentially disposed about the central vertical axis, the core being shaped such that a free space in the casting cavity not occupied by the core substantially resembles a shape of the cast part.   
   
   
       19 . The method of  claim 18 , wherein one end of the pouring cup forms an opening on an external surface of the cope and an opposite end of the pouring cup forms an opening on a wall of the casting cavity. 
   
   
       20 . The method of  claim 18 , wherein positioning the ceramic core includes positioning the core having a smooth surface finish in the casting cavity.